1. Field of the Invention
The present invention relates to communication systems, in particular, wideband code division multiple access (W-CDMA) systems with rate matching.
2. Description of the Related Art
Code Division Multiple Access (CDMA) is a channel access method used by radio communication technologies. CDMA enables signals to be multiplexed over the same channel by assigning each transmitter a code. The data bits are combined with a code so that the signal can only be intercepted by a receiver whose frequency response is programmed with the same code. The code changes at the chipping rate which is much faster than the original sequence of data bits. The result of combining the data signal with the code is a spread spectrum signal that resists interference and enables the original data to be recovered if the original data bits are damaged during transmission. CDMA technology optimizes the use of available bandwidth, and is used in communications such as ultra-high frequency cellular telephone systems.
Wideband CDMA (W-CDMA) is an International Telecommunications Standard (ITU) derived from CDMA technology. The code in W-CDMA technology is a wideband spread signal. W-CDMA is found in communications such as 3G mobile telecommunications networks. W-CDMA transmits on a pair of 5 MHz-wide carrier channels, whereas narrowband CDMA transmits on 200 kHz-wide channels. W-CDMA has been developed into a complete set of specifications. Specifically, details on W-CDMA multiplexing, channel coding and interleaving are described in “3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (3GPP TS 25.212)”, hereinafter referred to as “TS 25.212”. TS 25.212 defines rate matching parameter calculation schemes and a rate matching pattern algorithm.
In general, rate matching is used to match the number of bits to be transmitted to the number available in a single frame. The number of bits on a transport channel can vary between different time intervals. In the downlink the transmission is interrupted if the number of bits is lower than maximum. When the number of bits between different transmission time intervals in the uplink is changed, bits are repeated or punctured to ensure that the total bit rate after transport channel multiplexing is identical to the total channel bit rate of the allocated dedicated physical channels. Rate matching algorithms either repeat bits on a transport channel to increase the rate or puncture bits on a transport channel to decrease the rate. For example, rate matching is critical to meet certain quality of service (QoS) requirements in wireless communication systems.